External Iliac Veins

1. Overview

The external iliac veins are major blood vessels in the pelvic region that drain deoxygenated blood from the lower limbs and abdominal wall. They are an important part of the venous return system, carrying blood back to the heart from the lower extremities. The external iliac veins are formed by the union of the femoral vein and the deep femoral vein at the level of the inguinal ligament. These veins travel upward, passing through the pelvic cavity, and join the common iliac veins. The common iliac veins then empty into the inferior vena cava, which returns deoxygenated blood to the right atrium of the heart. The function of the external iliac veins is critical in ensuring that blood from the legs and lower body returns to the heart for oxygenation.

2. Location

The external iliac veins are located in the pelvic cavity, on either side of the body. They are formed by the union of the femoral vein and the deep femoral vein at the level of the inguinal ligament. The veins travel upward along the side of the pelvis, running posterior to the inguinal ligament and alongside the external iliac arteries. The external iliac veins ascend toward the abdominal cavity, where they eventually join the internal iliac veins to form the common iliac veins. The common iliac veins then merge into the inferior vena cava, which returns the blood to the right atrium of the heart. The external iliac veins are situated medial to the iliac arteries and are often closely associated with the psoas muscle in the pelvis.

3. Structure

The external iliac veins are large veins with a muscular structure designed to handle the return of blood from the lower limbs and pelvis. Key structural features of the external iliac veins include:

• Formation: The external iliac veins are formed by the convergence of the femoral vein and the deep femoral vein. The femoral vein drains blood from the lower limbs, while the deep femoral vein drains blood from the deeper structures of the thigh.

• Course: The external iliac veins ascend alongside the external iliac arteries, passing behind the inguinal ligament. They continue upward into the pelvic cavity, where they join the internal iliac veins to form the common iliac veins.

• Diameter and Length: The external iliac veins have a relatively large diameter, usually between 1.5 to 2 cm, but the size can vary between individuals. The length of the veins is typically around 8 to 10 cm, depending on the person's anatomy.

• Wall Composition: Like all veins, the external iliac veins consist of three layers:

  • Intima: The innermost layer of endothelial cells that provides a smooth surface for blood flow.

  • Media: The middle layer, composed of smooth muscle and elastic fibers, which allows the vein to accommodate changes in blood volume and pressure.

  • Adventitia: The outer connective tissue layer that provides structural support and helps anchor the veins to surrounding structures.

• Valves: The external iliac veins contain one-way valves that prevent the backflow of blood. These valves are crucial for ensuring that blood flows in the proper direction, particularly as it moves against gravity in the legs.

4. Function

The primary function of the external iliac veins is to collect deoxygenated blood from the lower limbs and abdominal wall and return it to the heart. Some key functions of the external iliac veins include:

• Venous return from the lower limbs: The external iliac veins are responsible for collecting blood from the femoral vein, which drains the lower limbs. The veins carry deoxygenated blood from the legs, pelvis, and groin area back toward the heart.

• Venous return from the abdominal wall: The external iliac veins also drain blood from the lower part of the abdominal wall through the deep femoral vein and other smaller veins that contribute to the venous return.

• Connection to the inferior vena cava: The external iliac veins merge with the internal iliac veins to form the common iliac veins, which then empty into the inferior vena cava. This pathway is essential for maintaining the blood flow back to the heart for reoxygenation in the lungs.

• Support of venous return during physical activity: During exercise, blood flow from the legs increases, and the external iliac veins play a vital role in returning the increased volume of deoxygenated blood to the heart. They work in conjunction with the valves in the veins to ensure efficient blood return despite the increased blood volume from the lower body.

5. Physiological Role(s)

The external iliac veins play several critical physiological roles that support the circulatory system as a whole. Some of these roles include:

• Oxygen and nutrient exchange: Although the external iliac veins themselves do not perform nutrient and oxygen exchange (a function handled by arteries and capillaries), they are essential for maintaining the flow of deoxygenated blood back to the heart, from where it will be pumped to the lungs for oxygenation.

• Prevention of venous stasis: The external iliac veins help prevent venous stasis (blood pooling) in the lower limbs. By efficiently returning blood to the heart, they contribute to the overall regulation of blood pressure and circulation in the lower body.

• Maintaining venous pressure: The external iliac veins contribute to maintaining the venous pressure of the lower body. By ensuring smooth blood flow through the venous system, they prevent excessive pressure buildup, which can lead to conditions like varicose veins or deep vein thrombosis (DVT).

6. Clinical Significance

The external iliac veins are clinically significant because they are essential for the venous return from the lower limbs and pelvis. Disorders affecting these veins can lead to serious health conditions. Some key clinical conditions associated with the external iliac veins include:

• Deep vein thrombosis (DVT): DVT is a condition in which blood clots form in the deep veins of the legs, including the external iliac veins. This can lead to swelling, pain, and potentially life-threatening complications, such as pulmonary embolism, if the clot dislodges and travels to the lungs. Treatment involves anticoagulation therapy, compression stockings, and, in some cases, surgery.

• External iliac vein thrombosis: Thrombosis in the external iliac veins occurs when a blood clot forms in one of these veins. It can cause swelling, discomfort, and reduced circulation to the lower limbs. Treatment may include anticoagulation therapy, thrombolytic therapy, or surgical intervention to remove the clot and restore blood flow.

• Varicose veins: Varicose veins are swollen and twisted veins that occur when the valves in the veins malfunction, causing blood to pool. The external iliac veins can be affected by varicosities, which can lead to discomfort, swelling, and other complications. Treatment for varicose veins includes compression therapy, sclerotherapy, or surgery in more severe cases.

• Aneurysm: An aneurysm in the external iliac vein occurs when the vein wall becomes weakened and dilated. This condition can cause discomfort and swelling and may lead to more severe complications, such as rupture and internal bleeding. Surgery may be necessary to repair the aneurysm and restore proper venous circulation.

• Pelvic venous congestion: The external iliac veins are part of the venous system that drains the pelvis. Conditions like pelvic venous congestion syndrome, which results from impaired blood flow in the pelvic veins, can cause chronic pelvic pain and discomfort, particularly in women. Treatment involves managing underlying causes and may include embolization or surgical interventions to reduce venous pressure.

The external iliac veins are critical for returning blood from the lower extremities and pelvis back to the heart. Dysfunction in these veins can lead to serious vascular conditions, including deep vein thrombosis, varicose veins, and aneurysms. Early diagnosis and treatment are essential to manage these conditions and prevent complications that can affect overall cardiovascular health.